Behavior therapy, i.e., exposure and response prevention (E/RP), is considered the psychological treatment of choice for obsessive-compulsive disorder (OCD). This treatment entails 3 weeks of daily 1-2 hour sessions (15 total sessions) in which feared situations are confronted with therapist supervision (exposure), and ritualizing is curtailed (respone prevention). However, because of the large time commitment needed to undertake E/RP, many individuals with OCD are either unable or unwilling to begin treatment. With the specific goals of testing the efficacy and durability of a less intensive E/RP protocol that might decrease treatment refusal rate, we propose a 3 year controlled treatment study to compare 15 sessions of daily E/RP delivered over 3 weeks to 15 sessions delivered twice per week over 7.5 weeks. A mid-treatment assessment (after 8 sessions) will also be included to determine whether fewer sessions of daily treatment are needed to achieve symptom reduction. The patients will be 25 adults with a DSM-IV diagnosis of OCD. The primary outcome measure is the Yale-Brown Obsessive- Compulsive Scale. Assessments conducted by evaluators blind to treatment status will take place at pretreatment, mid-treatment, posttreatment, and three and six month follow-up.